The invention relates to apparatus for immobilizing a working shaft at a predetermined angular position, and concerns apparatus comprising an electric clutch motor whereof the coupling member which is transmissively connected to the working shaft may be coupled electromagnetically to a constantly driven main driving spindle of the clutch motor and/or to a braking abutment, for the purpose of driving the working shaft at a preset working speed of revolution under the action of a regulator affected by the controlling difference between the actual speed of revolution measured and the preset speed of revolution.
In the case of positioning drives of this nature, the working shaft, the speed of revolution of which is governed during operation, is braked upon initiation of the immobilizing action from the working speed of revolution to a preset and relatively low switch-off r.p.m. and then kept at the switch-off r.p.m. by the regulator until an element, being a so-called synchronizer, which is transmissively coupled to the working shaft, comes into action and initiates the final braking operation from the switch-off r.p.m. to zero.
Known positioning drives (e.g. DT-AS 1,291,014 = GB-PS 1,150,932, and DT-AS 1,613,350) which operate on the principle defined in the foregoing, either lack of satisfactory quality of control (i.e. and excessive stoppage period and/or inadequate stopping precision), or are relatively costly and consequently of limited application.
The invention is based on the problem of devising a positioning drive which renders it possible to obtain a high quality of control and low cost.